Company's Repurchase Activities (Parenthetical) (Detail) - shares shares in Thousands	Dec. 31, 2017	Sep. 30, 2017
Capital Unit [Line Items]
Company's common units authorized for repurchase	7,344
Private Transaction
Capital Unit [Line Items]
Company's common units authorized for repurchase	2,450	2,450

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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